The present invention relates to a system and method for mooring a floating vessel to the sea floor. More particularly, the invention relates to a system and method in which two separate sections of a mooring leg, one of which is connected to the vessel and the other of which is secured to the sea floor, are joined together by a connection and tensioning device and the mooring leg is adjusted to a desired length by cross-pulling one of the sections through the tensioning device.
A prior art mooring system for a floating production, storage and offloading (“FPSO”) vessel is shown in FIG. 1. This mooring system, which is commonly referred to as a direct-connect mooring system, includes a number of mooring legs M which are connected between the FPSO's turret and an anchoring device which is embedded in the sea floor, such as a pile.
Once the mooring legs are connected to the FPSO, they must be tensioned to the desired length. In certain prior art mooring systems, this is accomplished by pulling the proximal ends of the mooring legs through corresponding chain stoppers on the turret using a heavy-duty winch on the FPSO. However the chain stoppers and heavy-duty winch add cost and complexity to the FPSO.
In the direct-connect mooring system illustrated in FIG. 1, each mooring leg is tensioned by first cutting it to a desired length and then connecting it to a short chain section which has previously been attached to a corresponding universal joint on the turret. When the FPSO is installed in deep water, each mooring leg comprises a relatively long vertical run. Consequently, the force required to connect the mooring leg to its corresponding chain section is manageable. However, in shallower waters the mooring legs comprise relatively short vertical runs. Consequently, more force must be used to connect the mooring lines to the FPSO. Depending on the depth of the water, therefore, this connecting force may become unmanageable.